Cadherins are a superfamily of calcium-dependent cell adhesion molecules (CAMs) (for review, see Munro et al., In: Cell Adhesion and Invasion in Cancer Metastasis, P. Brodt, ed., pp. 17-34, R G Landes Co., Austin Tex., 1996; Rowlands T M. et al (2000) Rev. Reprod. 5: 53-61, Nollet F. et al (2000) J. Mol. Biol. 299: 551-572). All cadherins appear to be membrane glycoproteins that generally promote cell adhesion through homophilic interactions (a cadherin on the surface of one cell binds to an identical cadherin on the surface of another cell), although cadherins also appear to be capable of forming heterotypic complexes with one another under certain circumstances and with lower affinity.
There are many different types of cadherins. The most extensively studied group of cadherins is known as the classical, or type I, cadherins. Classical cadherins have been shown to regulate epithelial, endothelial, neural and cancer cell adhesion, with different cadherins expressed on different cell types. All classical cadherins have a similar structure. Classical cadherins are composed of five extracellular domains (EC1-EC5), a single hydrophobic domain (TM) that transverses the plasma membrane (PM), and two cytoplasmic domains (CP1 and CP2). The calcium binding motifs DXNDN (SEQ ID NO:1), DXD and LDRE (SEQ ID NO:2) are interspersed throughout the extracellular domains, and each 110 amino acid region that contains such motifs is considered a cadherin repeat. The first extracellular domain (EC1) contains the cell adhesion recognition (CAR) sequence, HAV (His-Ala-Val), along with flanking sequences on either side of the CAR sequence that play a role in conferring specificity. Synthetic peptides containing the HAV sequence and antibodies directed against such peptides have been shown to inhibit classical cadherin-dependent processes (Munro et al., supra; Blaschuk et al., J. Mol. Biol. 211:679-82, 1990; Blaschuk et al., Develop. Biol. 139:227-29, 1990; Alexander et al., J. Cell. Physiol. 156:610-18, 1993; Makrigiannakis. et al. (1999) Am. J. Pathol. 154: 1391-1406; Wilby et al. (1999) Mol. Cell. Neurosci. 14: 66-84; Schnädelbach et al (2000) Mol. Cell. Neurosci. 15: 288-302; Williams et al. (2000) J. Biol. Chem. 275: 4007-4012; Schnädelbach et al. (2001) Mol. Cell. Neurosci. 17: 1084-1093; Erez et al. Exp. Cell Res. 294: 366-78; see also U.S. Pat. Nos. 6,031,072; 6,169,071; 6,417,325).
Cadherins that contain calcium binding motifs within extracellular domain cadherin repeats, but do not contain an HAV CAR sequence, are considered to be nonclassical cadherins. At least six groups of nonclassical cadherins have been identified as well several other cadherins that are not classified within the six groups These cadherins are also membrane glycoproteins. Type II, or atypical, cadherins include OB-cadherin (cadherin-11; see Getsios et al., Developmental Dynamics 211:238-247, 1998; Simonneau et al., Cell Adhesion and Communication 3:115-130, 1995; Okazaki et al., J. Biological Chemistry 269:12092-12098, 1994), cadherin-5 (VE-cadherin; see Navarro et al., J. Cell Biology 140:1475-1484, 1998), cadherin-6 (K-cadherin; see Shimoyama et al., Cancer Research 55:2206-2211, 1995; Shimazui et al., Cancer Research 56:3234-3237, 1996; Inoue et al., Developmental Dynamics 211:338-351, 1998; Getsios et al., Developmental Dynamics 211:238-247, 1998), cadherin-7 (see Nakagawa et al., Development 121:1321-1332, 1995), cadherin-8 (see Suzuki et al., Cell Regulation 2:261-270, 1991), cadherin-12 (Br-cadherin; see Tanihara et al., Cell Adhesion and Communication 2:15-26, 1994), cadherin-14 (see Shibata et al., J. Biological Chemistry 272:5236-5240, 1997), cadherin-15 (M-cadherin; see Shimoyama et al., J. Biological Chemistry 273:10011-10018, 1998), and PB-cadherin (see Sugimoto et al., J. Biological Chemistry 271:11548-11556, 1996). For a general review of atypical cadherins, see Redies and Takeichi, Developmental Biology 180:413-423, 1996; Suzuki et al., Cell Regulation 2:261-270, 1991; Nollet F. et al, (2000) J. Mol. Biol. 299: 551-572.
Other examples of nonclassical cadherins include LI-cadherin (see Bemdorff et al., J. Cell Biology 125:1353-1369, 1994), T-cadherin (; see Ranscht, U.S. Pat. No. 5,585,351; Tkachuk et al., FEBS Lett. 421:208-212, 1998; Ranscht et al., Neuron 7:391-402, 1991; Sacristan et al., J. Neuroscience Research 34:664-680, 1993; Vestal and Ranscht, J. Cell Biology 119:451461, 1992; Fredette and Ranscht, J. Neuroscience 14:7331-7346, 1994; Ranscht and Bronner-Fraser, Development 111:15-22, 1991), protocadherins (; e.g., protocadherins 42, 43 and 68; see Sano et al., EMBO J. 12:2249-2256, 1993; GenBank Accession Number AF029343), desmocollins (e.g., desmocollins 1, 2, 3 and 4; see King et al., Genomics 18:185-194, 1993; Parker et al., J. Biol. Chem. 266:10438-10445, 1991; King et al., J. Invest. Dermatol. 105:314-321, 1995; Kawamura et al., J. Biol. Chem. 269:26295-26302, 1994), desmogleins (e.g., desmogleins 1 and 2; see Wheeler et al., Proc. Natl. Acad. Sci. USA 88:4796-4800; Koch et al., Eur. J. Cell. Biol. 55:200-208, 1991), and cadherin-related neuronal receptors (see Kohmura et al., Neuron 20:1137-1151, 1998).
Most studies of nonclassical cadherins have focused on atypical or type II cadherins. The structure of these cadherins is similar to that of the type I cadherins, but they do not contain the CAR sequence, HAV. Furthermore, functions mediated by the atypical cadherins may be diverse. For example, cadherin-5 (also referred to as VE-cadherin) appears to be involved in endothelial cell adhesion and cadherin-6 (also referred to as K-cadherin) may be involved in embryonic kidney cell adhesion and is up-regulated in kidney cancer. Cadherin-15 also appears to play a role in the terminal differentiation of muscle cells.
OB-cadherin, which is also known as cadherin-11, is another atypical cadherin (Getsios et al., Developmental Dynamics 211:238-247, 1998; Okazaki et al., J. Biol. Chem. 269:12092-98, 1994; Suzuki et al., Cell Regulation 2:261-70, 1991; Munro et al., supra). This cadherin can promote cell adhesion through homophilic interactions. OB-cadherin does not contain the classical cadherin cell adhesion recognition sequence, HAV. A unique feature of OB-cadherin is the existence of two alternatively spliced isoforms: a full-length form with a cytoplasmic domain that interacts with catenins; and a truncated form that lacks most of the cytoplasmic domain (Feltes et al., Cancer Research 62:6688-6697, 2002). The truncated OB-cadherin variant is also shed from the cell surface and can be found deposited in the extracellular matrix surrounding the cells.
The acquisition of OB-cadherin expression by invasive cancer cells may confer invasive and migratory properties on such cells, thus facilitating metastatic dissemination (Pishvaian et al (1999) Cancer Res. 59: 947-952; Nieman et al (1999) J. Cell Biol. 147: 631-643). Highly migratory cancer cells also express the truncated form of OB-cadherin (Feltes et al An alternatively spliced cadherin-11 enhances human breast cancer cell invasion. Cancer Res. 2002 Nov. 15; 62(22):6688-97.). OB-cadherin levels are also high in stromal cells and osteoblasts (Shibata et al., Cancer Letters 99:147-53, 1996; Simonneau et al., Cell Adhes. Commun. 3:115-30, 1995; Matsuyoshi and Imamura, Biochem. Biophys. Res. Commun. 23:355-58, 1997; Okazaki et al., J. Biol. Chem. 269:12092-98, 1994). High levels of OB-cadherin expression in osteoblasts and stromal cells, as well as in cancer cells, may promote adhesion of cancer cells to secondary sites i.e. may promote homing of metastases.
OB-cadherin mediates adhesion between osteoblasts and lack of OB-cadherin (e.g., in OB-cadherin null mice) causes reduced bone density (Kawaguchi et al., Journal of Bone and Mineral Research 16:1265-1271, 2001). These findings indicate that OB-cadherin is important for the activity of osteoblasts, and in this way may be important for regulating bone turnover. In the context of bone metastasis, the normal balance of osteoblast and osteoclast activity that constitutes bone turnover is subverted by the cancer cells, leading to bone destruction accompanied by cancer growth (Mundy, Nature Reviews Cancer, 2:584-593, 2002). Disruption of bone turnover is also a feature of other bone diseases such as osteoporosis, Pagets disease and the like. OB-cadherin-mediated interactions may be important for the maintenance of proper bone turnover, and may be instrumental in the promotion of bone destruction in bone disease and metastasis. In cancers derived from bone cells, OB-cadherin levels may be altered, suggesting a role for this cadherin in the progression of cancers such as osteosarcoma (Kashima et al., American Journal of Pathology 155:1549-1555, 1999). OB-cadherin-mediated cell-cell contact stimulates expression of vascular endothelial growth factor (VEGF) members (Orlandini and Oliviero, Journal of Biological Chemistry 276:6576-6581, 2001). VEGFs are a family of secreted growth factors that function as stimulators of angiogenesis and lymphangiogenesis, processes that are important for the growth of primary tumors and their metastatic spread. The VEGF family includes VEGF-A (also known as VEGF and vascular permeability factor), VEGF-B, VEGF-C, VEGF-D and other related proteins (for review see Dvorak (2002) J. Clin. Oncol. 20:4368-4380). In some invasive cancer cells, OB-cadherin is not only found at sites of cell-cell contact, but also in lamellopodia-like projections which do not interact with other cells. These observations suggest that OB-cadherin may also play a role in modulating cell-extracellular matrix interactions.
OB-cadherin is also expressed in other specific cell types. A role for OB-cadherin in neuronal function was indicated by the observation that OB-cadherin-deficient mice have modified behavioral responses (Manabe et al., Molecular and Cellular Neurosciences 15:534-546, 2000). In adipocytes, OB-cadherin is the only known expressed cadherin. OB-cadherin is therefore likely to mediate adhesion between adipocytes, and it is likely to be an important regulator of adipogenesis. Cells of the related lineages encompassing pericytes (also known as the peri-endothelial cell), vascular smooth muscle cells and myofibroblasts also express OB-cadherin. Pericytes are contractile cells which are similar to smooth muscle cells. They encircle the endothelial cells of blood vessels. Pericytes are involved in maintaining the structural integrity of blood vessels (Hanahan, Science 277:48-50, 1997; Lindahl et al., Science 277:242-245, 1997). Loss of pericytes causes blood vessels to regress. Vascular smooth muscle cells encircle larger blood vessels and regulate blood flow. Myofibroblasts are cells that play important roles in the wound healing process. OB-cadherin is also expressed by cells of the immune system such as CD4+CD8+ thymocytes (Munro et al., Cellular Immunology 169:309-312, 1996). Collectively, these and other observations underscore the importance of OB-cadherin as a target for the development of novel agents for treating human disease.
Notwithstanding these recent advances, OB-cadherin function remains poorly understood at the biological and molecular levels. Accordingly, there is a need in the art for identifying agents involved in modulating OB-cadherin-dependent functions and processes, such as cell adhesion, cell migration and cell invasion and for the development of further methods employing such sequences to modulate processes having relevance to human disease conditions, such as cancer cell adhesion, invasion and/or metastasis. The present invention fulfills these needs and further provides other related advantages.